Conan O'Brien explains why he ditched signature hairstyle

Conan O'Brien finally explained the story behind his viral slicked-back hairstyle, revealing that a painful scalp sunburn forced him to cover his hair with oil while it healed.

The comedian shared the story during an episode of his Conan O'Brien Needs a Friend podcast, saying the mishap happened after attending the grand opening of the Obama Presidential Center in Chicago with his wife, Liza Powel.

O'Brien said he carefully applied sunscreen to his face before spending more than three hours outdoors and initially thought he had avoided getting burned.

"I was so glad that I put the sunblock on," he recalled, adding that he even noticed fellow guests Stephen Colbert and David Letterman looking noticeably sunburned.

However, a few days later, he realised something was wrong.

Conan O'Brien says scalp sunburn left him rubbing oil into his hair

The former late-night host said his scalp soon began burning and flaking badly.

"I feel like my skull is on fire," O'Brien said, explaining that scratching his head caused flakes to fall "like a snow globe."

He later learned he had suffered a scalp sunburn despite having a full head of hair.

To treat it, O'Brien said someone advised him to rub oil into his scalp, which resulted in the slicked-back hairstyle that surprised fans during his recent interview with Molly Shannon.

"I come in and I look like I'm in Sha Na Na. I'm a grease ball," he joked.

His assistant David Hopping admitted he wasn't a fan of the new look, while co-host Sona Movsesian said she actually liked it.

Before wrapping up the story, O'Brien offered viewers one simple piece of advice: "Wear a hat."